1985-12-09 Well Field Capacity AnalysisWELL FIELD CAPACITY ANALYSIS
FOR THE
JOINT POWERS WATER BOARD
HANOVER, FRANKFORT, ST. MICHAEL, AND ALBERTVILLE
DECEMBER 1985
BY
EUGENE A. HICKOK AND ASSOCIATES
545 INDIAN MOUND
WAYZATA, MINNESOTA 55391
I hereby certify that this report was prepared by me or under my direct
supervision and that I am a duly registered Professional Engineer in the State
of Minnesota.
<.� ,w� ��/9�'Y.,S /-� 37
John C. Lichter, P.E. Date Minnesota Registration No.
TABLE OF CONTENTS
Page
I. INTRODUCTION 1
II. DESCRIPTION OF PROJECT 2
III. GROUNDWATER MODELING RESULTS 3
IV. CONCLUSIONS AND RECOMMENDATIONS 5
V. QUALIFICATION STATEMENT 6
VI. REFERENCES 7
I. INTRODUCTION
This project was authorized by the Joint Powers Water Board to investigate
additional sources of water supply and the impact on existing facilities serving
the four member units of government.
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II. DESCRIPTION OF PROJECT
The members of the Joint Powers Board agreed that an additional source of water
supply is necessary to supplement the one existing supply well located east of
County Road 19 in Frankfort Township. Centralized treatment of water may be
necessary at some future date and it was decided to investigate locating a new
well adjacent to the existing well. If this was determined to be feasible,
water transmission costs to a future centralized treatment facility would be
minimal.
Location of a new well adjacent to the exsisting well will impact the drawdown
and capacity of the existing well. The purpose of the project was to simulate
this situation (the existing and new well) using a computer model.
Data was available to calibrate the model in the form of a pumping test
conducted on the original well in 1978. This data was tabulated and entered
into the model together with existing well log data for the production well and
observation wells 1 and 2. The site of the new well was chosen to be the
northwest corner of the existing property owned by the Joint Powers Water Board
(see Figure 1). Aquifer transmissivity and other characteristics were developed
for input to the model based on past work by E. A. Hickok and regional data
available from the United States and Minnesota Geological Surveys.
Elevations of well head casings were not available, so approximate elevations
were used. Pump setting and rating curves were also not available to compare
with model results at the time of this study.
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III. GROUNDWATER MODELING RESULTS
A. DESCRIPTION OF THE MODEL
This study was performed using a groundwater contouring program developed and
written by Professor Otto Strack, University of Minnesota. The model calculates
groundwater elevations (potential surfaces) by solving for points on a grid and
drawing contours to fit the grid data. By repeating this process for each
influence in the area and summing the solutions, the model generates a completed
drawdown contour map.
Description of in situ conditions: The area of study lies atop a thickness
sequence of glacial till, moraine, and reworked river sediments. The depth of
the sediments range from 400 feet at the production well to 300 feet at
observation well 2. This difference is due to 100 feet of uneroded shale. The
static water elevation in the area is approximately 908 feet (NGVD). This gives
a saturated thickness of 340 feet at the pumping well and observation well 1,
while only 240 feet at observation well 2. Due to this fact, a saturated
thickness of 240 feet was chosen so the area to the north could be more
accurately modeled.
— Several assumptions have been made in order to generate a model. First, all
wells were assumed to have an elevation of 968 feet above sea level (NGVD).
— Second, the static water elevation was set at 908 feet. Third, the saturated
thickness was assumed to be 240 feet, which reflects the higher bedrock at
observation well 2. Fourth, the production wells are considered 100 percent
— efficient. This assumption must be made in order to satisfy the equations used
in the program. The actual efficiencies are approximately 70 percent. This
causes the contours very close to the wells to be high. Fifth, regional flow
was assumed to be negligible.
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The first contour map generated was used for calibration (see Figure 2). Note
the field data indicated the water elevation in observation well 2 of 902.97 feet
and the computer model gives it a value of approximately 903 feet. Values close
to the production well are artificially high due to the fact the well is assumed
to be 100 percent efficient. Also, an effective hydraulic conductivity of
65 feet/day has been used to produce this match. This gives a transmissivity
of 117,000 gallons per day/foot. This indicates the sediments are still well
suited for water production. This value is lower than the transmissivity
calculated in 1978 because it is an average taken over a large area and not a
spot value taken from one point.
Figure 3 shows the effect of the second pumping well located in the northwest
corner of the property. This second well was assigned a pumping rate of 1,000
gallons per minute. From this contour map and the fact the well will only be
70 percent efficient, the combined drawdowns at either pumping well will be
approximately 25 to 30 feet below the static water level.
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IV. CONCLUSIONS AND RECOMENDATIONS
A. CONCLUSIONS
1. The aquifer model indicated an additional drawdown of 5-10 feet at the
existing production well would be expected by pacing a second 1,000 gallons
per minute well in the northwest corner of the well site property.
2. The effect on the current capacity of the existing well would be minimal
from the second well.
3. The estimated total drawdown from static water level at each well is
estimated to be approximately 25-30 feet.
4. Surface geophysics and test borings outside the well site area are probably
not necessary at this time. However, a single test boring should be placed
near the proposed well location to verify model assumptions and physical
conditions.
B. RECOMMENDATIONS
1. Based on the computer modeling results, it appears that construction of
a new well in the existing well field is a feasible alternative.
2. Modeling results indicate that certain further work previously proposed such
as geophysical studies and other off -site investigation is probably
unnecessary.
3. Pump settings, rating curves, and discharge pressures shoudl be further
examined to verify the desirability of this alternative.
4. A test boring is recommended to confirm model results at the proposed well
site.
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V. QUALIFICATION STATEMENT
This analysis has been conducted using reasonable care, professional judgement,
available data, and modern techniques for this application. It is possible that
field conditions may vary from those anticipated and thereby could alter the
results of this analysis.
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VI. REFERENCES
Lindholm, et al. Water Resources of the Crow River Watershed, South -Central
Minnesota. Hydrologic Investigation Atlas HA- 2 Unite tates Geological
Survey and the Minnesota Department of Natural Resources. 1974.
Strack, O.D.L. "Groundwater Mechanics: Groundwater Contour Fortran Computer
Model." Unpublished course text. University of Minnesota. 1984.
E. A. Hickok and Associates. Joint Powers Pump Test Results. 12-inch
production well south of Albertfille. February 10, 1985.
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1 ST.
MICHAEL
JOINT POWERS WATER BOARD
THEORETICAL COMBINED
DRAWDOWN CURVE
SCALE IN FEET
E.A. HICKOK & ASSOCIATES
HYDROLOGISTS - ENGN EERS
MINNEAPOLIS - MINNESOTA
DEC. 1985
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